feat: Ensure storageEngine implements correct interface

In order to prevent implementation errors, we want to check that
storageEngine implements the correct methods

This replies to #1483 (comment)

packages/cozy-pouch-link/src/localStorage.js

@@ -9,6 +9,7 @@ export const LOCALSTORAGE_ADAPTERNAME = 'cozy-client-pouch-link-adaptername'
 
 export class PouchLocalStorage {
   constructor(storageEngine) {
+    checkStorageEngine(storageEngine)
     this.storageEngine = storageEngine
   }
 
@@ -220,3 +221,23 @@ export class PouchLocalStorage {
     await this.storageEngine.setItem(LOCALSTORAGE_ADAPTERNAME, adapter)
   }
 }
+
+/**
+ * Throw if the given storage engine does not implement the expected Interface
+ *
+ * @param {*} storageEngine - Object containing storage access methods
+ */
+const checkStorageEngine = storageEngine => {
+  const requiredMethods = ['setItem', 'getItem', 'removeItem']
+
+  const missingMethods = requiredMethods.filter(
+    requiredMethod => !storageEngine[requiredMethod]
+  )
+
+  if (missingMethods.length > 0) {
+    const missingMethodsString = missingMethods.join(', ')
+    throw new Error(
+      `Provided storageEngine is missing the following methods: ${missingMethodsString}`
+    )
+  }
+}

packages/cozy-pouch-link/src/localStorage.spec.js

@@ -0,0 +1,48 @@
+import { PouchLocalStorage } from './localStorage'
+
+describe('LocalStorage', () => {
+  describe('Type assertion', () => {
+    it('should throw if setItem method is missing', () => {
+      expect(() => {
+        new PouchLocalStorage({
+          getItem: jest.fn(),
+          removeItem: jest.fn()
+        })
+      }).toThrow(
+        'Provided storageEngine is missing the following methods: setItem'
+      )
+    })
+
+    it('should throw if getItem method is missing', () => {
+      expect(() => {
+        new PouchLocalStorage({
+          setItem: jest.fn(),
+          removeItem: jest.fn()
+        })
+      }).toThrow(
+        'Provided storageEngine is missing the following methods: getItem'
+      )
+    })
+
+    it('should throw if removeItem method is missing', () => {
+      expect(() => {
+        new PouchLocalStorage({
+          getItem: jest.fn(),
+          setItem: jest.fn()
+        })
+      }).toThrow(
+        'Provided storageEngine is missing the following methods: removeItem'
+      )
+    })
+
+    it('should throw if multiple methods are missing', () => {
+      expect(() => {
+        new PouchLocalStorage({
+          getItem: jest.fn()
+        })
+      }).toThrow(
+        'Provided storageEngine is missing the following methods: setItem, removeItem'
+      )
+    })
+  })
+})